Pulse transmitter



Sept. 24, 1946. E. LABIN PULSE TRANSMITTER 2 Shets-Sht 1 Filed Aug. 12,1941 F IG.2.

IN VEN TOR 671/15 143/ A TTORNE Y Sept. 24, 1946. LABlN PULSETRANSMITTER Filed Aug. 12, 1941 2 S hets-Sheet 2 TME 'l I INT/Enron'/7/LE LAB/N W c O M. n M m F I j F T 0 v 3 I44 B 0 T l mfi 5% Nfifi fiQQQ 5 5 W W 7 m b g m m m TV a p a 3 a Q$Q 55k wmfi wax 53k ATTORNEY.

Patented Sept. 24, 1946' PULSE TRANSMITTER Emile L abin, New York, N.Y., ass ignor to International Standard Electric Corporation, New 4York, N. Y., a corporation of Delaware Application August 12, 1941,Serial No. 406,499

Claims.

The present invention relates generally to apparatus for producing brieftrains of oscillation and particularly to apparatus for producing briefhigh power trains of high frequency oscillations.

There are many uses for such'a source of brief trains of high frequencyoscillations, among them being their use in distance finding apparatusfor generating high power impulses. In distance finding apparatus it isnecessary and desirable to produce wave trains of large peak power sothat;

these wave trains may be directly radiated without amplification, whilestill giving a large amount of radiated power and hence a large usefuloperating range for the. apparatus.

It is an object of my invention to provide an eflicient apparatus fordelivering brief wave trains of high power'waves.

' It is a further object to provide such an apparatus suitable fordelivering high power brief wave trains of ultra-high frequency waves,the.

wave trains being of accurately controlled length and spacing. r

' It is a further object to provide such an apparatus which when poweredby a plate supply source of given voltage is capable of delivering wavetrains of substantially higher power than could be delivered byconventional .apparatus using a plate supply of said given voltage.

' It has: heretofore. been proposed to produce high power trains ofoscillations by applying to the plateof a suitableoscillation generator.tube, brief high power impulses derived from a B supi I be as much asten times the plate supplyvoltage.

ply of moderate voltage by a controlled amplifier having an inductancein its output circuit. In

. accordance with thissystem the current in an' inductance connected inthe plate circuit of the amplifier tube is interrupted by means ofcontrol signals of the desired form applied to the grid of this tube andobtained from a separate low power impulse generator. This systemoperates fairly satisfactorily, but it has;several disadvantages:

(a) During the period of charging current flow in the inductance, a highpositive voltage must be applied to the grid of this amplifier tube inorder that the plate current may approach the maximum emission currentof the tube. g

, (b) Because of the grid current which flows during the chargingperiod, the amplifier or generator which drives the amplifier in (a),must supply a considerable amount of power to a low impedance (theeffective grid resistance time being from 100 to .500 ohms).

at this (0) During the period of discharge of the inductance, theinstantaneousplate voltagefmay .vention; Y

The negative grid voltage consequently must be raised to several timesthe normal cut-off value to insure that thetube isblocked duringthedischarge or pulsing period.

It is both difiicult and expensive to build an amplifier which will passa wide band of frequencies (to allow a very fast blocking action),deliver alarge amount. of power into a low resistance and supply a highnegative voltage to an infinite resistance.

For medium power installations it is possible to reduce some of theabove difiiculties by employing'aflpentode tube as the amplifier tubeconnected to the inductance. However, for high powerapplicationspentodes are costly and introduce circuit complications.

It is an object of my invention to provide a source of brief waveftrainsof high power and high frequency waves while'avoiding the diflicultiesabove mentioned. J 'According to my invention, I provide as the sourceof plate supply for a high frequency oscillator an impulse generatorcomprising an amplifier tube having an inductance coil in its outputcircuit and means for coupling the inductance coil to the grid circuitof the amplifier tube. In

the preferred embodiment of my invention I employ a triode as anamplifier tube.

.It is a further object of my invention to provide an improved impulsegenerator capable of producing impulses of high peak power.

It is another object of my invention to provide a self-excited impulsegenerator capable of producing impulses of high peak power.

It is another object of my invention to employ in said high powerimpulse generator a triode as an amplifier-generator tube.

It is another object of my invention to provide apparatus for accuratelycontrolling the duration of high frequency pulses.

Myinvention will be more clearly understood by referring to theaccompanying drawings wherein:

Fig. 1 illustrates an impulse transmitter for delivering briefwavetrains of high power in accordance .withmy invention; I 1

Fig. 2 is a diagram used in explaining my in- Fig. 3 shows a circuitemployed in operation tests; I

Figs. 4a, 4b, 4c and 4d are diagrams used in describing the operation ofthe impulsegenerator of m n en o I I I Fig.5 illustrates an embodimentof y invention wherein a high frequency oscillator is controlled by bothpositive and negative impulses from an impulse generator.

Fig. 1 discloses an impulse generator connected as the power supply foran oscillator. The impulse generator comprises a vacuum tube 2 having aplate 3, a control grid i and an electron emissive cathodei5=which maybe directly Or indirectly heated. An inductance 6 is connected in serieswith the energy source 1' in the plate circuit of the tube 2 between theplate 3 and the cathode 5. circuit and the grid circuit is obtained bymeans of coil 8 which is inductively:coupled-to the-inductance B andwhich may be considered'as one coil of the transformer 6, 8. The isprimarily determined ance timing circuit consisting of condenser 9 andresistance l0. As shown, the condenser and resistance H! are in serieswith the grid 4, but they may, instead, be connectedin series with thecathode 5. I

-When the inductance 6 is charging, "that is, when current is flowing intube2,'- the plate end of the inductance is negative with-respect totheother end of the inductance. When the inductance is discharging (no tubecurrent), the .re- 'verse polarity exists.

-In practice, the load 'resistance for inductance '6 will vary between10,000 ohms for 10 to microsecond impulses, and 2,000ohms for -l to.2microsecond impulses. 'Thisload resistanceis of' the same'or'der as theplate resistanceofmanycommonly employed oscillator tubes. In thepreferred embodiment of my inventioml employ the impulse generator asthe ;plate voltage supply for an oscillator. The impulse generator .mayalsoact as'the power supply for any other power electrode-such as thescreen grid of the oscillator tube. In Fig. 1, one end of the inductance'coil 6 of the impulse generator lSCOIlIlECtEdTtO the mid-point of apair of lecher Wires 36zand 31. These lecher wires 35 and B'Lserve totune :the plate circuit of the tubes 38 andi139, .and-the lecher wiresare connected to the plates or:power electrodes 40 and Moi the tube. Thegrids :or control electrodes 42-and 43 areconnected to .a 'pair oflecher wires M1 and 45 whichserveto tune the grid circuit=0f't1l6'tubeSl38. and;39. A resistor '46 serves as a'biasing resistor.odesor electron emissive electrodes '48 and '49 are connected to acommon return point.

During the charging and steady state .periods of the impulse generatorthe "oscillator comprising the tubes tive. When the inductance 6discharges, .the tubes 38 and 39 and their accompanying circuits areenergizedandoscillations are;produced. It will thus be seen that highfrequency energy is produced for an interval substantially equal to thedischarge time of theinductancecoil 6. Actually the oscillator willcease to oscillate'before the inductance coil '6 is completelydischarged, and the high frequency pulse'w'ill-be a 'little shorter thanthat delivered by'the inductance coil 6 to a resistance load.

The oscillator stage is preferably coupled to transmitting systemdirectly, .but it may also be coupled to an amplifier or amplifiers andthen to a transmitting system. .As. shown iniFigg-ljthe oscillator iscoupled by means of loop 35 tothe transmitting system I. It is to beunderstood that although'I have shown a push-pull'oscillator as apreferred type other types of'osc-illator's' may "be employed.

Positive feedback betweenthe plate 7 .38 and 39 'is inopera-' inductancewith a negative resistance.

Although impulse generators and oscillators are both known, I shalldescribe the impulse generator employed in accordance with my inventionin more detail in order that my invention may be more clearlyunderstood.

The use of inductive coupling between the plate andgrid circuits has theeffector" shunting the For the present purposes'the circuit shown inFig.1 may be considered during the charging period as "equivalent to aninductance in parallel with a .15' pulsing rate by thecapacity-resistvnegativeresistance and with the capacities of thecomponents of the circuit. 'A circuit consisting of inductance, capacityand resistance, which'is capable of oscillating at high values ofresistance, may become aperiodic if the resistance is;small, even thoughnegative. If Re is the resistance for critical damping, the circuit'will be aperiodic as long as the shunt or parallel resistance remainsbetween +Rc and -P.c. When the circuit is made aperiodic by damping witha negative resistance (-Rc), the operation is not at all normal. Anysmall current increase develops into a very rapid and large exponentialincrease. From the moment at which the current begins to rise, itcontinues torise to its ab solute limit, always in the same directionand with'increasing speed. Similarly, a decrease in current will alsofollow an exponential law.

When the inductance 6 is charging and this inductance is connected tothe oscillator as a plate supply for the tubes-thereof, the efiect ofthe oscillator tubes may be neglected since, as pointed out above, thepolarity of the potential on the inductance is such that the plates ofthe tubes are at a negative potential with respect tothe cathodes andthe resistance of the tubes may, therefore, be consideredas infinite.When, however, the inductance discharges, its-polarity reverses, and theinductance discharges into the tubes as well as the circuit componentsof the generator itself. During the discharge, the oscillator tubes actsubstantiallyas a resistance load.

The discharge 'of the inductance begins .at the instant that the platecurrent is blocked. The plate current of the tube 2 having :beenblocked,.the resistance of tube 2 may be considered as infinite, andconsequently, the .zcircuit consists of the inductanc Gin parallel withthe inherent resistanceof the oscillator (if substantially resistive)and a-capacity consisting substantially of the capacities of tube 2 andthe oscillator, the.distributed'capacity'of coils 6 and 8, condenser land other capacities to ground. From the theory of parallel inductance,capacity and resistance circuits, it is known that the discharge of the.inductance fi into the oscillator (considered as a 'load) will be madein a minimum time and with a maximumpeak power if the circuit constantsare given critical values which satisfy the equation.

Under these conditions, the discharge of the inductance will follow acurve l'ikethat shown in Fig. 2.

For-abetter understanding of the operation of the impulse generator acycle of operation will be described as follows:

(a) Charge.-As soon as the grid condenser '9 almost completelydischarges through the resistance l0, plate current will begin to flow.This current will increase continuously to a value 'near=the'satur-ation current value ior the t'ubezi. Atthefsame'timethe'voltage at the Jplata'alil will decrease dueto the reactance drop acrossinductance. 6; andthegrid' voltage will increase positivelyudue to thefeedbackbetween .the. grid, and plate circuits giving a large gridcurrent flow. The power furnished to the grid circuit is obtained fromthe plate voltage source.

(b) Discharge.,-The increase in plate current will cease when the platecurrent approaches the. saturation current of the tube. At this time thegrid voltage, which has been held at a high ..Yalue ,due to theinductive coupling between the plateandgridjcircuits, will begin todecrease :causing a decrease in the'plate current. The direction ofplate current; variation will then re- Yerse,1and this effect becomescumulative causinggthe platecurrent to decrease rapidly. The gridvoltage will decrease and finally become negative.

be stopped in a Very short time producing a high voltage'attheterminals. of the inductance Theiresultis that the plate current 6.-;If; the coupling between coils 6 and 8 is properly adjusted, ahighrnegative voltage apthe inductance there will be no voltage acrosscoil 8, and therefore, dueto the charge on condenser 9, plate currentwill notflow. The condenser will discharge through resistance l0, andfinally plate current will again fiow and the cycle will ,be repeated.

For best operation the tube 2 shouldhave a. high saturation current toallow high values of charging current, shouldv have a highmutualconductance to provide properdamping for cir-' cuit component impedancevalues-other than the critical values and for negative resistance valuesand should be well evacuated in order to withstand the high peak voltagewhich is produced during the discharge of. 00116. It may be seen thatwith the exponential variations which take place the inducance will storalarge. amount of energy during its charge, and this energy will bereleased during a very short period A peak voltage as high as 20,000volts may be realized across the plate inductance coil with a powersupply voltage of only 1000 volts. Accordingly, the circuit componentsof the impulse generator and associated apparatus must be carefullyinsulated, and one of the chief points of concern is .7 .the insulationbetween the plate lead of the tube and other apparatus. It has beenfound possible with well evacuated low power tubes having thoriated'filaments to use peak currents and peak voltages from 10 to times thenormal operating values without damaging the tubes or Y shortening thelives of the tubes. These. values correspond to peak powers from 100 to400 times -the normal. tube rating.v I 1 .7

.In order to' observe the operationof the im- .-pulse. generator anoscillographic analysis was made. with the circuit shown in- Fig. 3. Inthis figure 22 is a high vacuum tube having a plate "or anode 23, a grid24am a cathode 25. Con 'nected to the anode 23is an inductance 26, andthe grid 24.; is coupled to. the-inductance, 26 by coil .128 shuntedbyresistance 2| Resistance [9 and:

*6 theshighvacuum diode '20 in. series therewith form a .load for theinductance. Resistance 30 in parallel-with condenser 29 serves asatiming circuit to control the impulse frequency. .Source 1 2.1, whichmaintains a potential of about 350 .lvolts, serves as a power supply forthe generator. .1 Meters 3|. and 33 serve to indicate thecurrents instherespective circuits, and resistances 32 and 34. are'providedas voltagesources for an oscilloraph;

. In the circuit-of Fig. 3 the-following elements were employed:

Tube '22 I 'a, 'type Ell-'3 receiving tube manufactured by N. V.{Philips Gloeilampenfabrieken I of Eindhoven, Holland; Th operatingcharacteristics are:

- Amplification factor 20 Plate resistance ohms 2000 Grid resistance do100 Plate voltage volts 350v Tube 20 a rectifier of the so-called typewhich is widely sold in the United States.

Condenser 29 a 1 mfd. condenser Resistance 30 a rheostat variable from1000 ohms to 200,000 ohms.

Resistances 32 and 344 ohm fixed resistors.- Resistances I'Sand 2|loading resistors. Inductance 26 an inductance of about 15 millihenrysand requiringa critical resistance of W about 8,000 ohms. "Q

With the above apparatus it has been found 'pQSSlbIB to'produce currentsof about 1 ampere and; peak voltages as high as 6,000 volts, the peakpower being about {i kilowatts. V The development of 4 kilowatts peakpower with a small receiving tube and a 350 volt plate supplyillustrates the advantage of the present invention. These results for asmall tube were duplicated on a much larger scale with larger triodessuch' as the Eimac tube T2,000 manufactured by Eitel-McCullough, -Inc.,jof San Bruno, California. Tubes of this latter type, using mycircuit, can deliver 3 micro- 45' second pulses of 30,000 volts in a3,000 ohm resistance with a D. 0. power supply of only 6,000 volts;Thiscorresponds toa peak power of. 300

- With the circuit shown in Fig. 3, a transformation ratio of 0.5 and acoupling coefiicient of 0.8, the oscillograms shown in Figs. 4a, 4b, 4cand 4d were obtained. These oscillograms show that at'the time A, thegrid condenser, has discharged sufficiently for plate current to flow.The flowin plate current decreases the plate voltage due to the dropacross the inductance 26 and-causes the grid voltage to become positive.At this time grid current Will begin to flow. I

' During-the time interval from B to C, the plate current approachessaturation, the plate voltage 1 approaches the voltage of the platesupply, the grid voltage reaches a positive maximum and the grid currentremains substantially constant at its original value. When plate currentsaturation isreached at the point C, the inductance Zfidischargesproducing amaximum of voltage, the grid voltage suddenly becomes neg-,ative and "the flow of grid current is stopped. After the discharge ofthe inductance 26 all of the current" and'voltages except the gridvoltage assume their steady state value, the grid voltage reaching itssteady state value only after-the discharge of the grid condenser. Theseoscillograms bear ,out the series of operations set forth in connectionwithFig. -1.

--'discharge of the inductance -26. ---sistance it in the circuit, thegrid voltage will \During :the .oscillographic analysis ofitheiimpulselgenerator operation, it was found that the ratio oftransformation .and the ccoupling .co- :efficient 'ihave.considera'blelinfluence :on the Yeperation .of .the generator..It1was.:found:.that for ..*small .values :of "transformation ratio thegrid .current is excessive;andsubtracts from the plate current. .Forlarge valueskof transformation ratio the grid excitationisinsumcient.InJorder to obtain a maximum value of peak plate current, .Iiprefer touse transformation :ratios between 0.5 and 0.8.

:The leakage reactance-of-the coupling trans- ,fo'rmer .afiectsboth'thecleng 'th of the charging ,period and the ratio of ithe, platevoltage to. the grid voltage. 'I have 'found that .thelbestoperatingresults are not obtained with coupling values near unity. -By -loweringthecoeflicient of coupling slightly-that is,by introducing anappreciable amount of leakage reactance, the moment at which the gridvoltage reaches its peak value will be retarded. It is desirable thatthe grid voltage and the anode voltage increase simultaneously 'forunder this condition high peak currents are obtained. The leakagereactance provides a convenient means for regulating the relationbetween the anode voltage and the grid voltage. I have found thatpreferable .values for the coefiicient of coupling arebetweenapproximately 0.6 and 09.

If the transformer has a transformationratio of approximately and if noprecautions are taken-the grid'voltage'during the discharge ofthe-inductance -26 w'ill'be approximately equal to one-halfoithe-instantaneous plate voltage. Suchahigh grid voltage=wil1- causearc-over between-the filament and the grid of the tube and will lowerthe maximum peak voltage obtainable. -For cut-oi? at the peak platevoltage it is *only necessary that the grid voltage'be equal to-thepeak'plate divided-by the amplification factor or the tube. Theamplification 4 factor of tubes commonlyemployedin amplifiers is usuallyconsiderably more than two. Accordingly, the-grid voltage may be'reducedto-a'value less than one-half'ofthe anode voltage.

'In accordance with'my invention, I provide a resistance 2| connectedacross the terminal of the-grid coil 28 of the transformer--2B-28 shownin -Fig.'-3. Due tothe effect of the transformer leakage reactance, theresistance 2! across the grid coil will cause the negative grid" impulseto be' li-rnited'tothe desired value-without changing the maximumvoltage obtainableacross the plate coil 26.

The 'useof the resistance "2| in the grid cirin the grid circuitmay'besubstantially elim- "inated. It has been found that unless a resistancesimilar to theresistance 2| is-employed, oscillationsmay continue in thegrid circuit after'the With the reincrease-smoothly'in the positivedirection after the 'dischargecf the inductance, -and'therefore, "theregularity of the'pulsing cycle'will be assured. V

The length of the transmitted high frequency pulse" may be controlledbyapplying 'a negative impulse'to the grid of the-oscillator. Therefore,-in accordance with a further'feature of my in verition I -'-employ thenegative impulse which controls the impulse generator for controllingthe high frequency oscillator. Fig. '5'i1lustrates one embodiment of myinvention wherein high .frequency oscillator Pis controlled by anegative impulse from the Iimpulse generator. L In .this figure theoscillator and generator are substantially .theisame asithose showniinFig. 1. Since 5 :the negativegimpulsei produced .at the grid A-and thepositive impulse produced by the coil G are produced simultaneously, theLnegative impulse which is appliedto' the oscillator must bedelayed. Thenegative impulse may, -.for example; be applied to the grids42.=and'43zby means of block- .ing condenser :Bfl andthettime delay:circuit consisting of coil 5| :and :condenser "52 connected to cne-endofresistahcelfi. The time delayin- -troduced 'may :be regulated 'by:adjusting the values rof thezcoil-il and the condenser 52. The

ratio of the coil 5| to the condenser 52 is preferably i substantiallyequal to the squared 1 value of the resistance lfi. The condenser '53'isa by- :pass condenser. Although I: have shown'the 'timing circuit 9,ill! in series with the cathode, itis tobe understood that Istilllconsider that the inductance 6 and the source'l are connected inserieszbetweenzthe-anode 3 and-the cathode 5.

.While I'have'described particular embodiments 0i myinvention, for'purposes of illustration, it will be understood that wariousmodifications thereof maybe made without departingirom the scope of myinvention.

What I claim is:

-1. A pulse transmitter comprising an oscillator comprising a vacuum:tubehaving-a power electrode, an electronemissive electrode and acontrol electrode, an output circuit coupled-to-said power-electrode, aninput "circuit coupled to "said contro1'electrode and=meansforieedingenergy from' 'said output-to said input circuit, means for supplyingoperatingipotential to-said power electrodes comprising an impulsegenerator comprising a vacuum tube having an anode, a control 40electrodeand an electron emissiveelectrode, an i output circuit coupledto said anode, an input circuit coupled t'o'said grid and means forfeeding energy from saidlast+mentioned output circuit to saidlast-mentioned input circuit, anddirect current #eonnections forcoupling said last-mentioned output circuit to the power electrode ofsaid oscillator.

. 2. 'A pulse transmitter comprising an'oscillator comprising a vacuumtube having an :anode, a

'50 control-grid and a'cathode, atunedinput circuit I connected to saidcontrol grid, a tuned'output circuit connected to said anode-and meansfor feeding energy from said outputcircuit to said input .circuit, animpulse generator comprising a vacuum tube-havingan anode, acontrolgridand a cathode, an inductanceconnected in series with said generatoranode and cathode, means for coupling said inductance 'to said generatorgrid -and tirning means connected between a said gen- 50 erator. gridan'd cathode, and direct current connecting means for .connecting incoupling relation -said oscillator anode to the junctionotsaidinductance andisaid generator anode.

3. A pulse transmitter according to :claim 5 wherein said means forcoupling :saicl inductance and said timing means arefrespectively 'acoilinductively coupled to saidi inductance 'anda condenser andresistance.iin-rparallel, ;-said :coupling meansi and said timing emeansbeing.connected :in series between said generator :cathode rand saidgenerator grid.

4. A: pulse Ltransmittericomprising a'.push-pu1l Voscillator-comprising! a pair ofivacuum tubes .each having an anoole, Iagrid and :a 1 cathode, :.said "anode and 'said .gridlbeing :capacitivelyxzcoupled.

tuned lecher wires connected between the anodes of said tubes, tunedlecher wires connected between the grids of said tubes, biasing meansconnected between said grid lecher wires and a common ground point andmeans for connecting said cathodes together and to said common groundpoint, an impulse generator comprising a vacuum tube having an anode, agrid and a cathode, an inductance coil connected between said generatoranode and said common ground point, a resistance and a condenser inparallel forming a timing circuit, a coil inductively coupled to saidinductance, a resistive impedance connected in parallel with said coil,said coil and resistive impedance forming a coupling circuit and saidcoupling circuit and said timing circuit being connected in seriesbetween said generator grid and said generator cathode, a source ofenergy supply and means for connecting said source between saidgenerator cathode and said common ground point, and means for connectingfor direct current coupling the end of said inductance connected to saidgenerator anode to said anode lecher wires.

5. A pulse transmitter comprising an oscillator comprising a vacuum tubehaving an anode, a control grid and a cathode, a tuned input circuitconnected to said control grid, a tuned output circuit connected to saidanode and means for feeding energy from said output circuit to saidinput circuit, an impulse generator comprising a vacuum tube having ananode, a control grid and a cathode, an inductance connected in serieswith said generator anode, means for coupling said inductance to saidgenerator grid and timing means connected at the cathode terminal ofsaid generator to control the potential of said generator grid, directcurrent connecting means for connectin said oscillator anode to thejunction of said inductance and said generator anode, and a time delaynetwork connected between said oscillator grid and said generator grid.-

6. A pulse transmitter according to claim 4 further comprising atime-delay network connected between said grid lecher wires and saidgenerator grid, said net-work comprising a blocking condenser and a coilconnected in series between said generator grid and said grid lecherwires and a further condenser connected between said last-mentioned coiland said common ground point.

7. A pulse transmitter according to claim 4 wherein said oscillatorbiasing means comprises a resistance and further comprising a time-delaynetwork connected between said grid lecher wires and said generatorgrid, said network comprising a condenser and a coil connected in seriesbetween said generator grid and said grid lecher wires and a furthercondenser connected between said last-mentioned coil and said commonground point, the ratio of the magnitude of the last men- 10 tioned coilto the magnitude of said further condenser being substantially equal tothe squared value of the magnitude of said biasing resistance.

8. A pulse transmittercomprising an oscillator comprising an inputcircuit, an output circuit, a vacuum tube having a power electrode,means for connecting said circuits to said vacuum tube and means forfeeding regenerative energy from said output circuit to said inputcircuit, an impulse generator comprising a vacuum tube having an anode,a control electrode and a cathode, means for coupling said anode to saidcontrol electrode, an inductance, a source of direct current energy,means for connecting said source and said inductance in series and tosaid anode, said impulse generator producing a series of impulses havinga peak voltage greater than the voltage of said direct current sourceand means for feeding said impulses to said power electrode of saidoscillator comprising a conductive connection from said power electrodeto the end of said inductance connected to said anode.

9. A pulse transmitter comprising an oscillator comprising a vacuum tubehaving an anode, a

control grid and a cathode, a tuned input circuit connected between saidcathode and said grid, a tuned output circuit connected between saidcathode and said anode, and means for feeding regenerative energy fromsaid output circuit to said inputcircuit, an impulse generatorcomprising a vacuum tube having an anode, a control grid and a'cathode,an inductance, a source of direct current energy, means for connectingsaid source and said inductance in series between said anode and saidcathode, a coupling coil inductively coupled to said inductance, thetransformation ratio and the coefiicient of coupling between saidinductance and said coil being between 0.5 and 0.8 and 0.6 and 0.9respectively, a timing circuit comprising a condenser and a resistanceconnected in parallel, means for connecting said coil and said circuitin series between said grid and said cathode, a further resistance,means for connecting said further resistance in parallel with said coil,means for connecting said oscillator anode to the end of said inductanceconnected to said generator anode, and means for connecting saidoscillator cathode to the other end of said induct ance.

10. A pulse transmitter comprising an oscillator, a vacuum tube in saidoscillator having a power electrode, an electron emissive cathode and acontrol electrode, an impulse generator, means for feeding positiveimpulses from said generator to said power electrode and means forfeeding negative impulses to one of said electrodes, said latter meanscomprising a time delay circuit to delay said negative impulses withrespect to said positive impulses.

EMILE LABlN.

